Co-sputtered Ta\(_2\) O\(_5\) -ZrO\(_2\)  coatings were produced with the custom-developed so-called Grand Coater (with a volume of 10 m\(^3\) ) used to coat the mirrors of the Advanced LIGO, Advanced Virgo and KAGRA detectors [1]}, [2]}, [3]}. Prior to deposition, the base pressure was less than 10\(^{-7}\)  mbar. Ar gas was fed into the sputtering source while O\(_2\)  gas was fed directly into the vacuum chamber, for a total working pressure of \(2 \times 10^{-4}\)  mbar. Energy and current of the sputtering Ar ions were of the order of 1 keV and 0.1 A, respectively. During deposition, the co-sputtered Ta\(_2\) O\(_5\)  and ZrO\(_2\)  particles impinged on substrates heated up to about 120 \(^\circ \) C.
